This invention relates generally to fluidic metering, proportioning and blending systems, and more particularly to a system provided with a variable Venturi structure whose movable element is automatically shifted as a function of the mass-volume of the fluids passing through the structure to provide outputs representative of the volume and density or mass of the fluids.
A system in accordance with the invention is applicable to internal combustion automotive engines to so proportion the ratio of combustion air to fuel as to maintain an optimum ratio thereof under varying conditions of load and speed throughout a wide operating range, thereby attaining higher combustion efficiency, significantly increased fuel economy and reduced emission of pollutants.
The function of a carburetor is to produce the fuel-air mixture needed for the operation of an internal combustion engine. In the carburetor, fuel is introduced in the form of tiny droplets in a stream of air, the droplets being vaporized as a result of heat absorption in a reduced pressure zone on the way to the combustion chamber whereby the mixture is rendered inflammable. In a conventional carburetor, air flows into the carburetor through a Venturi tube and a fuel nozzle within a booster Venturi concentric with the main Venturi tube. The reduction in pressure at the Venturi throat causes fuel to flow from a float chamber in which the fuel is stored through a fuel jet into the air stream. The fuel is atomized because of the difference between air and fuel velocities.
Although most carburetors today use double and triple Venturis to multiply suction forces, the fixed sizes of these Venturis, usually determined by the mid-range capacity of the engine, gives rise to fuel induction throughout approximately one-half the automotive operating range. The lack of Venturi-carburetion action at idle and slow speeds makes it necessary to introduce fuel downstream of the Venturi by means of the high vacuum developed by partially-open throttle plates. At higher speeds and power, air bleeds are needed to moderate excessive enrichment by the higher Venturi velocities. And under maximum power when the Venturi vacuum is moderate, additional fuel is supplied by means of power jet, stepped needle valves or auxiliary barrels.
Thus existing techniques for regulating the fuel-to-air ratio throughout the existing range from idle to full power, represent, at best, a compromise dictated by the above-noted limitations, fuel efficiency being poor at idle, low speeds and high power. Moreover, the overcome acceleration "flat spots" encountered during transitions in driving modes, throttle-actuated fuel pumps are employed to spray additional fuel into the air stream, thereby rendering the system even less efficient.
Other popular carburetors make use of the manifold vacuum to operate air-flow valves coupled to stepped or tapered needle valves, fuel being introduced eccentrically in non-Venturi passages. Existing systems of fuel injection for internal combustion engines produce air-fuel mixtures by means of pressurized fuel nozzles for timed or continuous spray into the air stream. A hybrid system called "throttle-body injection" utilizes pulsed electric injectors directly into the air stream above the throttle plates. All such systems rely on gathering data on a variety of operating engine variables, and the continuous monitoring of these factors, this data being fed to a mini-computer to produce the electric pulses that control the intermittent supply of fuel. These systems to not fully take into account the requirements for gasifying the fuel-to-air mixture; and even though they act to manipulate the fuel-to-air ratio, combustion efficiency is sacrificed.
The behavior of an internal combustion engine in terms of operating efficiency, fuel economy and emission of pollutants is directly affected both by the fuel-air ratio of the combustible charge and the degree to which the fuel is vaporized and dispersed in air. Under ideal circumstances, the engine should at all times burn 14.7 parts of air to one part of fuel within close limits, this being the stoichiometric ratio. In the actual operation of a conventional system, richer than stoichiometric is required at idle and slow speeds for dependable operation, whereas leaner than stoichiometric is desirable at higher speeds for reasons of economy. The employment of Lambda oxygen exhaust sensors and feedback controls to maintain the stoichiometric ratio for catalytic control of emissions is at the expense of performance and economy.
Maximum fuel economy and minimum emission of pollutants have heretofore been considered to be mutually exclusive due to the practical limitations of presently available systems. These limitations stem from the inability to "gasify" liquid fuel in air from idle to full speed and power before ignition in the engine. By the term "gasify" is meant fuel that has been dispersed, vaporized and homogenized to a gaslike quality. At or about the stoichiometric ratio of such gasified air-fuel mixtures, the most complete combustion with minimum emissions will result.
In my above-identified copending application of which the present case is a continuation-in-part, there is disclosed a closed loop engine control system acting to maintain that ratio of air-to-fuel which represents the optimum ratio for the prevailing condition of engine speed and load. The system includes a variable-Venturi carburetor which atomizes and disperses the fuel in the air whereby the system not only brings about a marked improvement in fuel economy but also substantially reduces the emission of noxious pollutants.
In the closed-loop system disclosed in my copending application, the variable Venturi structure is constituted by a cylindrical casing and a cylindrical booster coaxially disposed therein whose internal surface has a Venturi configuration to define a primary passage. This primary booster may consist of two concentric venturis in a step arrangement. Interposed between the booster and a section of the casing wall having an external Venturi configuration is an axially shiftable spool whose internal surface has a Venturi configuration to define between the booster and the spool a variable secondary passage whose effective throat size depends on the axial position of the spool. A tertiary passage is defined between the outer surface of the spool and the casing section. Air passing through the Venturi structure flows through all three passages.
An air-fuel dispersion is fed by a nozzle into the primary passage to intermingle with the air flowing therethrough to form an atomized mixture which is fed into the secondary passage to intermingle with the air flowing through the throat thereof, from which secondary passage the mixture intermingles with the air flowing through the tertiary passage, the total thereof being fed into the intake manifold of the engine.
The closed loop system disclosed in my copending application adjusts the position of the axially-shiftable spool by the application of the differential-pressure signal taken at the stationary tap in the tertiary passage at the casing wall to a fluidic amplifying and servo system, thereby controlling fuel flow proportionate to air flow throughout the operating range.
The system includes a vacuum amplifier constituted by a vacuum-regulating valve in a vacuum chamber coupled to the intake manifold of the engine and controlled by a diaphragm and spring assembly which responds to the pressure differential vacuum signal developed between the input and throat of the Venturi. The vacuum chamber yields a strong vaccum output directly proportional to the Venturi pressure differential signal.
The amplified vacuum output is applied to a bidirectional, spring-return vacuum motor operatively coupled to the Venturi spool which acts to axially shift the spool in a direction and to an extent bringing about the desired ratio of air-to-fuel, either by proportioning the fuel flow by the direct effect of the Venturi pressure differential acting on the fuel or by regulating, in accordance with the Venturi pressure differential, the fuel fed to a nozzle or injector in those applications where a pressurized fuel feed is desirable.